Oh! I am sorry PhiLho,
Part 1: Blinking Sound
Here is a link of similar kind of application
"also fail to see where colors can be erased or mixed in your sketch."
PhiLho, I haven't done it yet but this is I have to do when I would get rid of this problem.
Part 2: Sound Interaction
"Is the sound intended to reflect the state of the canvas, or should it be driven by the actions of the user? "
Yes it would be driven by the user action but not as you have mentioned "Position of the mouse" instead when user draw a stroke then sound plays.
Another thing, after drawing a stroke it would keep blinking until it gets erased.
Part 3:
These are the features I'll add in this application
A. Thickness of the stroke will control the pitch of the sound
B. Size of the stroke will control the volume of the sound
C. Instead of using "sine wave sound" I'll use some mp3 or wav file to play a piece of music when a any stroke gets drawn.
Anyway , I am trying to figure it out by myself but please give any suggestion if you have ........
Thanks ,